Method of calibrating light delivery systems, light delivery systems and radiometer for use therewith

ABSTRACT

A light delivery device ( 10 ) having a light source ( 12 ) and a variable aperture unit ( 18 ) is temporarily connected by a light guide ( 24; 24, 26 ) to a radiometer ( 38 ) for detecting irradiance of the delivered light. The light delivery device has a memory ( 30 ) for storing irradiance levels. The light delivery device is calibrated by adjusting the aperture to each of a series of predetermined settings, obtaining from the radiometer a corresponding series of delivered light irradiance levels measured thereby, storing the irradiance levels and aperture settings in memory, and applying a best fit algorithm to the irradiance measurements and aperture settings. Thereafter, a desired irradiance level can be set by selecting the best fit aperture setting. Output intensity levels may be measured at the same time as the irradiance levels and used to compensate for light source degradation when setting a desired irradiance level.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional patentapplication No. 60/638,344 filed Dec. 23, 2004, the entire contents ofwhich are incorporated herein by reference.

DESCRIPTION

1. Technical Field

The invention relates to methods of calibrating light delivery systems,to the light delivery systems themselves and to radiometers for usetherewith and is especially, but not exclusively, applicable to lightdelivery systems for curing photosensitive materials.

2. Background Art

As discussed in the background section of U.S. Pat. No. 5,521,392(Kennedy et al.), commonly owned with the present invention, there arenumerous substances which are sensitive to light energy. The substancesof interest generally fall into two classes. The first class comprisessubstances which undergo polymerization in response to applied lightenergy. The second class comprises substances which produce a “singletoxidation molecule” in response to applied light energy. The secondclass of substances can be found in “photodynamic therapy” or“phototherapy” applications, while the first class of photo-sensitivesubstances are typically found in UV polymerization and photochemicalcuring of adhesives.

It is known that the time it takes to cure a photosensitive adhesive isinfluenced by two principal factors. The first factor encompasses thetype of adhesive and amount which is required for the application. Oncedetermined for the particular application, this factor remains fixed forthe application. The second factor affecting the cure time involves theamount of light energy being delivered to the cure the adhesive. It isalso known that the intensity of the light produced by the light sourcewill decrease over the life of the source. As the light source degrades,so will the amount of light energy being delivered to cure the adhesiveand therefore a longer exposure time is needed to properly cure theadhesive.

In some applications, it may be desirable to adjust the intensity levelinstead of the exposure time in order to provide a light energy outputwhich is optimum for a particular curing application. Moreover, it isusually desirable to be able to compensate for changes in the lightintensity levels produced by the light source which degrades throughoutits useful life.

U.S. Pat. No. 5,521,392 describes a light curing system for use withsuch photosensitive materials which provides continuous intensitymonitoring and adjusts the exposure time or intensity level, or both, tocompensate for output degradation in the light source and therebyprovide a constant light energy output, from the curing system, for agiven iris setting. The intensity level is measured at the output of alight delivery means of the light curing system. This signal is used bya controller to calibrate the internal continuous monitoring sensor.This allows the internal sensor to be calibrated periodically against aNIST traceable device.

It is desirable to calibrate each radiometer off-site according toindustry standards, so each radiometer is detachable so that it can beremoved for calibration and replaced temporarily with a spare radiometerwhich has already been calibrated. In a production setting, there may bemany light curing systems and hence many radiometers, especially whenthe substitutes are included. Calibration of these multiple radiometersis not only time-consuming but also may lead to undesirable differencesbetween the output intensity levels.

In a production setting, there is usually a need for a high degree ofconsistency between the output intensity levels of the curing systems.Different rates of degradation of the light sources and transmissionlosses of the light guides, as well as different rates of drift of theradiometers, may lead to undesirable differences between outputintensity levels of the different light curing systems.

The problem is compounded where several light curing systems are presetto the same output intensity or irradiance setting. As the light curingsystems degrade differentially, these settings may no longer be the sameand may require re-calibration, typically at least once per week andpossibly every day.

DISCLOSURE OF INVENTION

The present invention seeks to eliminate, or at least mitigate, thedisadvantages of the prior art, or at least provide an alternative.

According to a first aspect of the invention, there is provided a methodof setting an output level of a light delivery device (10) thatcomprises light-emitting means (12), light output means (24; 24, 26) fordelivering emitted light to a site to be irradiated, intensity controlmeans (16) for adjusting at least the intensity of the delivered light,and a memory unit (30) for storing data including parameters indicativeof intensity/power level, the light output means (24;24,26) beingtemporarily connected to a separate radiometer (38) having means fordetecting power levels of the delivered light, the light delivery device(10) and the radiometer (38) having respective control means (28,48) anddata communications means (34,36,54,56) for communicating datatherebetween, the method comprising a calibration sequence comprisingthe steps of:

-   (i) with the light output means (24; 24,26) coupled to the    radiometer (38), establishing data communications between the    control means (48) of the radiometer (38) and the control means (28)    of the light delivery device (10); at the light delivery device    (10).-   (ii) adjusting the intensity control means (16) successively to each    of a series of predetermined intensity levels; at the radiometer    (38):-   (iii) measuring a series of actual output irradiance levels    delivered by the light output means (24;24,26), each for a    respective one of said predetermined intensity levels;-   (iv) transmitting the actual output irradiance levels to the light    delivery device (10); at the light delivery device (10):-   (v) associating each of the actual output irradiance level    measurements with the corresponding intensity level parameters in    said memory unit.

The step of adjusting the intensity control means (16) successively toeach of a series of predetermined intensity levels may comprise settinga variable aperture unit thereof to each of a series of differentaperture openings, the stored parameters then comprising aperturesettings.

In preferred embodiments, the radiometer carries out steps (iii) and(iv) in response to a request from the light delivery device.

Preferably, when establishing communications, the radiometer acquiresfrom the light delivery device a unique identifier, such as its serialnumber, and associates the irradiance readings with that uniqueidentifier.

The radiometer may have means for determining the diameter of the lightdelivery means at its end coupled to said radiometer, the detected powerand the diameter then being used to compute the irradiance of thedelivered light, the computed irradiances being said actual irradiancelevels.

The radiometer may store effective diameters of a plurality of differenttypes of light delivery means indexed to a plurality of indicators eachunique to a corresponding said type, light delivery means of aparticular type having the same effective diameter, and the step ofdetermining the diameter then may comprise detecting a said uniqueindicator of said light delivery means connected to the optical inputport and using the detected indicator to retrieve the effective diameterfor that light delivery means from storage.

The unique indicator may be colour, and detection of said uniqueindicator then may comprise the step of determining the colour of acolour-coded adapter connecting the light delivery means to the opticalinput port, for example by means of a colorimeter in the radiometer.

According to a second aspect of the invention, there is provided amethod of setting respective output light irradiance levels of aplurality of light delivery devices to the same irradiance level usingthe same radiometer, each light delivery device comprisinglight-emitting means, output means for supplying the emitted light to asite to be irradiated, intensity control means (16) for adjusting atleast the intensity of the delivered light, a memory unit for storingparameters indicative of intensity levels and control means forcontrolling the intensity control means, the radiometer having datastorage means for storing data including light irradiance values, theradiometer and light delivery devices having data communications meansfor communicating data therebetween, the method comprising the steps of:

-   (i) manually adjusting a first light delivery device to deliver a    desired irradiance level at its output means;-   (ii) temporarily coupling the radiometer to the output means of the    first light delivery device and measuring said desired irradiance    level;-   (iii) storing said desired irradiance level in the memory of the    radiometer;-   (iv) temporarily coupling the radiometer to the output means of at    least a second such light delivery device, and transmitting said    desired irradiance level to said second delivery device via said    data communications means; and-   (v) storing the light irradiance value in the memory of the second    light delivery device for future use in normal operation.

Steps (iv) and (v) may be repeated for a plurality of other such lightdelivery devices.

Each of the light delivery devices may have means for monitoring forvariations in light output of its light-emitting means and the methodmay include the step of correcting the subsequent intensitylevels/aperture settings to compensate for variations in said lightoutput.

The data communications link may be established by way of wirelessinput/output ports of each light delivery device and radiometer,respectively.

According to a third aspect of the invention, there is provided aradiometer for use in setting output light delivered by at least onelight delivery device to a desired light irradiance level, said at leastone light delivery device comprising light emitting means, light outputmeans for supplying the emitted light to a site to be irradiated,intensity control means for adjusting at least the irradiance of thedelivered light, a memory unit for storing irradiance levels, and datacommunications means, the radiometer comprising:

-   -   means for measuring an irradiance level of light delivered by        said light output means of said light delivery device;    -   data communications means complementary to the data        communications means of the light delivery device; and    -   control means for establishing data communications with a light        delivery device coupled thereto and for outputting to said light        delivery device said desired light irradiance value from said        memory via the data communications means.

The radiometer may further comprise a storage unit for storingirradiance readings for one or more light delivery devices, indexedaccording to, for example, serial number of the light delivery deviceand the date/time of measurement.

The data communications means preferably are wireless.

The radiometer may have means for identifying that the light deliverymeans coupled to said radiometer has a particular diameter, and thecontrol means may then use the detected power and the diameter tocompute the irradiance of the delivered light, the computed irradiancesbeing said actual irradiance levels.

The unique indicator may be colour, and detection of said uniqueindicator then may comprise the step of using a colorimeter in theradiometer to detect the colour of a colour-coded adapter connecting thelight delivery means to the optical input port.

According to a fourth aspect of the invention, there is provided a lightdelivery device comprising light-emitting means, light output means fordelivering the emitted light to a site to be irradiated, intensitycontrol means for adjusting irradiance of delivered light; and controlmeans for controlling the intensity control means and for communicatingwith an external radiometer, the control means being operable to adjustthe intensity, successively, to a plurality of intensity levels and, foreach intensity level, communicate with the radiometer to obtain from theradiometer a corresponding series of actual irradiance levels measuredby the radiometer and store each irradiance value in a memory unit inassociation with the corresponding intensity level.

The intensity control means (16) may comprise a variable aperture unit(18) for selecting each of a series of different aperture openings toset the intensity level, the stored parameters then comprising aperturesettings.

The intensity control unit may function as a shutter and may compensatefor shutter opening and closing delays when determining exposure times.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription, in conjunction with the accompanying drawings, of apreferred embodiment of the invention which is described by way ofexample only.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block schematic diagram illustrating a light delivery systemcomprising a light delivery device and a radiometer temporarily coupledto it;

FIG. 2 is a perspective view of the radiometer;

FIG. 3 is a flowchart depicting the method steps performed by the lightdelivery device during its calibration; and

FIG. 4 is a partial schematic diagram illustrating a modification to theradiometer.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates a light delivery system comprising a light deliverydevice 10, for example a spot curing device, which, typically, is one ofa set of similar such light delivery devices, perhaps disposed along thesame production line. Thus, the light delivery device 10 comprises alight source unit 12, a bandpass filter 14, an intensity control module16 comprising a variable aperture unit 18 and stepper motor 20, a beamsplitter 22 and an output port 24 to which, in use, a light deliverymeans 26, specifically a light guide, can be connected. The light sourceunit 12 comprises a lamp 60, typically an arc lamp, in a reflective lamphousing 62.

The stepper motor 20 is controlled by a control unit 28 which comprisesone or more processors and an associated data memory unit 30 and isprogrammed (e.g. firmware) to control the operation of the lightdelivery device 10. The control unit 28 is coupled to a user interfaceand display unit 32, whereby a user can input commands and the controlunit 28 can display information. The control unit 28 also is coupled toan RS232 port 34 and a wireless (IrDA) port 36, through either of whichports it can communicate with an external radiometer 38. The controlunit 28 may also be coupled to an additional RS232 port 34′ forconnection to an external computer (86), as shown in broken lines inFIG. 1.

The light output of lamp 60 will deteriorate over time so the lightdelivery device 10 includes an intensity control system, specifically afeedback control system for correcting settings of the intensity controlmodule 16 to compensate. The feedback control system includes the beamsplitter 22 which, conveniently, is an angled quartz plate withanti-reflection coatings and which taps off 1-2% of the light passingthrough it and supplies it to a photodetector 64. The correspondingelectrical signal from the photodetector 64, which is proportional tothe power of the light at the output port 24, is converted by an A-Dconverter 66 to a corresponding digital signal S₀ which is supplied tothe control unit 28. As the lamp 60 degrades, and its output diminishes,the control unit 28 will apply a suitable correction when setting thesize of the aperture unit 18 so as to ensure that the light delivered tothe proximal end of the light guide 26 has the required intensity levelto provide a desired irradiance at the distal or output end of the lightguide 26. The variable aperture unit 18 is controlled by the steppermotor 20, the position of which is determined by step count commandsfrom the control unit 28, and may conveniently comprise a rotatableplate having apertures of different sizes arranged in a circle orspiral. The plate may also serve as a shutter. Alternatively, thevariable aperture unit 18 could comprise an iris.

The user interface and display unit 32 typically includes a lightemitting diode (LED) display and a set of pushbuttons for selecting aparticular mode of operation, and for adjusting the value of aparticular parameter according to selected mode. For example, thesebuttons allow the user to adjust the setting of the exposure time andthe intensity level, and store readings. The interface 32 unit may alsoinclude a series of indicator lights which are illuminated according tothe operation of the pushbuttons and state of the unit. For example,indicator lights may indicate that the lamp 60 is energized and theaperture is open.

When the mode selection pushbutton is operated to select a mode, thelight delivery device 10 will be set to one of two modes, convenientlydesignated “relative” and “absolute”. If the light delivery device 10has not been calibrated, which is the case whenever the light guide hasbeen removed and replaced, the system will be in “relative” mode, andthe display will show the aperture setting as a percentage of themaximum aperture. If the light delivery device 10 has been calibrated,as will be described later, the system will be in “absolute” mode andthe display will show a calibrated intensity level of the light passingthrough the beamsplitter 22 which is displayed as irradiance in W/cm².The user may change the level by operating pushbuttons until a desiredpercentage or irradiance level is displayed. Likewise, with the deviceset to “Timer” mode, the user may operate pushbuttons to adjust thedesired exposure time, specifically by setting a timer in the controlunit 28.

The radiometer 38 comprises an optical input port 40 to which the lightguide 26 is coupled by an adapter 42. Detection means 44, in the form ofa thermopile 44 disposed adjacent the port 40, detects the power of thelight from the light guide 26 and supplies corresponding electricalsignals to an analog-to-digital converter 46, which supplies thecorresponding digital signal S_(LG) to a control unit 48 of theradiometer 38. A data memory 50 coupled to the control unit 48 storesdata records and other information associated with the calibration ofthe light delivery device 10 (and other delivery devices).

The radiometer 38 also comprises a user interface and display unit 52,for communicating commands and information between a user and its owncontrol unit 48, and two input/output data ports, specifically an RS232port 54 and an IrDA port 56, for connection to the corresponding dataports 34 and 36, respectively, of the light delivery device 10 to enablethe exchange of data and signalling between the two control units 28 and48. The two data ports allow the system to be operated in either awireless mode or via a conventional cable connection. It should be notedthat only one of the data ports need be used at any given time. A RemoteInput Connector (RIC) data port 84 is provided to interface theradiometer 38 with other external radiometer devices 38′. The RS232 port54′ may also be used for connection with an external computer 86.

In most applications, the light guide 26 comprises a fiber optic cableor a liquid light guide which can be maneuvered around the work piece,either manually or by machine, e.g. a robotic arm.

Referring now to FIG. 2, the radiometer 38 comprises a housing 80 with afront panel having the user interface and display unit 52 (FIG. 1),which comprises a liquid crystal display (LCD) 52A and a series ofmembrane switches 52B for controlling the following modes and function:

-   -   RELATIVE/ABSOLUTE for selecting the relative and absolute        display modes alternatively (where, in absolute mode, the        radiometer 38 displays actual irradiance values and, in relative        mode, it displays irradiance values as percentages of a        reference value that may be the power at the point of entering        relative mode);    -   CAL for setting up and calibrating compatible delivery devices        to a specified irradiance; POWER/IRRAD for toggling between        power and irradiance measurements;    -   EXTERNAL for enabling the radiometer 38 to detect and measure        external radiometer devices when connected via a remote input        connector (RIC) 84;    -   STORE to save measurement data into a data log in memory 50 for        future retrieval by a personal computer via data port 54; and    -   ON for turning the radiometer 38 on.

The optical input port 40 and adapter 42 protrude from the top of thehousing 80. The wireless (IrDA) port 56 also is provided on the top ofthe radiometer 38, adjacent port 40. (If desired, when the R2000 iscoupled to a separate computer (RS232 second connection), the keypadcould be disabled).

Typically, the radiometer 38 will be used with light delivery deviceshaving different light guides, whose lengths and, more importantly,diameters and, hence, cross-sectional areas may differ. Light guides 26having the same cross-sectional area will each have the same type ofconnector, requiring a specific adapter to connect it to the port 40.Light guides having a different diameter will have a different type ofconnector and hence different adapter. Thus, there are several adapters,each colour-coded with a different colour that identifies the type oflight guide 26 with which it is used, and hence represents thediameter/area. The colour of each adapter is analysed by a calorimeter58 which is disposed adjacent the port 40. The colorimeter 58 brieflyilluminates a section of the adapter 42 with a white LED and, using acolour detection integrated circuit, detects the colour and conveyscorresponding RGB colour values to the control unit 48. The latter usesthe RGB colour values to access its memory 50 and retrieve thecorresponding area, the different adapter RGB colour values andassociated areas having been previously stored therein duringmanufacture. Typically, the radiometer 38 will detect and store thediameter/area of the light guide whenever the radiometer 38 is turned ONand/or when a light guide adapter is installed.

In normal use, with the radiometer 38 removed, the light delivery device10 provides a pre-determined amount of light energy to a work piece orobject (not shown) to be treated. The work piece may include aphotosensitive material which reacts to the applied light energy. Thecontrol unit 28 controls the amount of light energy applied to the workpiece according to pre-selected parameters determined from data inputtedby the separate radiometer 38, as will be described later, while it istemporarily coupled to the light delivery device 10 by means of a cableconnected between RS232 ports 34 and 54 of the light delivery device 10and radiometer 38, respectively (or by a wireless link if preferred).The radiometer 38 will usually have been calibrated off-site accordingto industry standards (e.g. NIST).

As mentioned above, if the light delivery device has not beencalibrated, its aperture settings will be determined as a percentage ofmaximum aperture open area and the control unit 28 will calculate andissue corresponding step counts to the intensity control module 16according to inputs via the user interface and display unit 32 or fromthe radiometer 38.

If the light delivery device 10 is to be used in absolute mode, asexplained previously, it must be calibrated so that a user, eithermanually or by way of a radiometer, can input a desired irradiance andthe light delivery device 10 will operate the intensity control module16 to select the aperture required to deliver that irradiance level atthe end of the light guide 26. In fact, even if the light deliverydevice 10 has been calibrated, whenever certain critical things changefor example the light guide or the lamp another calibration process willneed to be carried out.

Calibration is performed by coupling the light guide 26 to the opticalinput port 40 of the radiometer 38 and initiating automatic performanceof a series of irradiance measurements at ten predetermined apertureopenings distributed throughout the operating range. This calibrationprocedure will now be described with reference to Table II below and theflowchart shown in FIG. 3, the Table steps being referenced T1, T2, . .. and the flowchart steps being referenced 3.01, 3.02, . . . and so on.It should be noted that the flowchart depicts only part of thecalibration process in terms of functions of the light delivery device10, whereas Table II illustrates functions of both the light deliverydevice 10 and the radiometer 38. In the following description, thevarious commands or messages will be described as being exchanged by theradiometer 38 and the light delivery device 10, but it will beappreciated that it is their respective control units 28 and 49 thatcommunicate via the RS232 links.

With the optical port and data port of the radiometer 38 coupled to thelight guide and the data port of the light delivery device 10, theradiometer 38 checks the state of its “CAL” pushbutton and, if it isidle (i.e. not pushed), repeats the check periodically. In step T1, theuser initiates communications between the radiometer 38 and the lightdelivery device 10 by pressing the CAL-pushbutton to select thecalibration mode of the radiometer 38, whereupon the radiometer 38attempts to set up communications with the light delivery device 10 viathe RS232 link. The light delivery device 10 responds with a “ready”command (step T2), at which point communications have been established.In step T3, the control unit 48 requests the serial number of the lightdelivery device 10 which transmits it in step T4. On receipt of theserial number, the radiometer 38 stores it in its memory 50.

In step T5, the radiometer 38 sends a “SET” command to the lightdelivery device 10. This “SET” command may be a desired irradiance levelto which the light delivery device 10 is to be set for a subsequentcuring operation, but nevertheless will cause the light delivery device10 to enter the calibration mode and, in step 3.02 (see FIG. 3), displaya “CAL” icon. In step T6/3.03, the light delivery device 10 sends theradiometer 38 a command requesting the light guide area (LGA). In step3.04, the light delivery device 10 monitors for receipt of the LGA andrepeats the request (step 3.05). If a predetermined number of requestsfail to illicit the LGA, in step 3.06 the light delivery device 10 sendsan “abort” command and exits the calibration process. If desired, ofcourse, the radiometer could transmit the diameter rather than the LGA,and the light delivery device 10 could compute the area itself, orsimply apply a suitable scaling factor when calculating irradiance.

If, in step T7, the radiometer 38 transmits the light guide area (LGA),having previously determined it by using the colorimeter 58, asdescribed above, to identify the adapter colour, then looking up thecorresponding diameter in memory 50, and calculating the correspondingarea. On receipt of the area in step 3.04, the light delivery device 10adjusts the variable aperture means 18, in step T8/3.07, to the first ofthe ten predetermined aperture openings corresponding to preprogrammedcalibration set points, and leaves it open. This opening is actuallydetermined by a predetermined number of steps (step count) of thestepper motor 20 as determined and optimized during the design phase.The predetermined step counts for the various calibration points oraperture openings are preprogrammed into the memory 30 of the lightdelivery device 10.

In step T9, the radiometer 38 measures the power of the light receivedby its thermopile 44 and, using the light guide area (LGA), calculatesthe corresponding irradiance as W/cm² (by dividing the power by thelight guide area). After a certain “settling time” to allow the readingto stabilize, the light delivery device 10 sends a request to theradiometer 38 for the irradiance reading (step T10/3.08). In step T11,the radiometer 38 sends the irradiance reading to the light deliverydevice 10 and also stores this irradiance reading in its own memory 50,along with the serial number of the light delivery device 10, thecorresponding power as measured by its thermopile 44, the calibrationdate and the current time (in real time as opposed to lamp hours), asshown in Table I.

On receipt of the irradiance reading (in step 3.09), the light deliverydevice 10 stores it in its own memory 30 (step 3.12) in association withthe step count and the digital representation S_(o) of the intensityreading I_(o) of the light entering the light guide 26 via optical port24. In step 3.13, the light delivery device 10 determines whether or notirradiance readings have been taken for all ten calibration points. Ifthey have not, it returns to step 3.07, adjusts the aperture to the sizeappropriate to the next calibration point, and repeats steps T9-T12 and3.08-3.13 for the new calibration point. This cycle repeats until step3.13 indicates that all ten irradiance readings and ten correspondingintensity levels have been measured, whereupon, in step T14/3.14, thelight delivery device 10 sends a “Done” command to the radiometer 38 andreturns to its previous display mode.

The light delivery device 10 also determines whether or not the receivedirradiance values are valid. It does so by comparing each receivedirradiance value (after the first) to the previous one and ensuring thatthey differ from each other by a predetermined amount, i.e. as apercentage. If any of the received values is determined to be invalid,the calibration (CAL) procedure is aborted and an ABORT command sent tothe radiometer.

On receipt of the “Done” command, in step T15 the radiometer 38 exitsthe calibration sequence and returns to normal operation.

Once the light delivery device 10 has obtained the ten irradiancemeasurements, they are associated in the data memory 30 of the lightdelivery device 10 with ten corresponding values of the digital signalS₀ representing the intensity I₀ detected by the photodetector 64 (i.e.in the feedback control system) and the ten step counts associated withthe ten aperture settings, respectively.

The control unit 28 performs a “best fit” algorithm, e.g., a ten pointcubic-spline, twice, once upon the ten pairs of irradiance and digitalintensity values and once upon the ten pairs of irradiance and stepcount values. In each case, the control unit 28 determines coefficientsof the splice function linking step count with irradiance and intensityso that, when the light delivery device is being set to deliver a“desired” irradiance level, the inputted desired irradiance level I_(LG)can be used to determine both a corresponding step count and acorresponding intensity level I_(o). For both iterations of the spline,input arrays X (e.g. irradiance level) and Y (e.g. step count orintensity level) are used to determine coefficients A, B, C and D asfollows:y=Ay _(i) +By _(i)+1+Cy _(i) ^(II) +Dy _(i) ^(II)+1  (1)and the coefficients are given by

$\begin{matrix}{A = \frac{x_{i + 1} - x}{x_{i + 1} - x_{i}}} & (2) \\{B = {1 - A}} & (3) \\{C = {\frac{1}{6}\left( {A^{3} - A} \right)\left( {x_{i + 1} - x_{i}} \right)^{2}}} & (4) \\{D = {\frac{1}{6}\left( {B^{3} - B} \right)\left( {x_{i + 1} - x_{i}} \right)^{2}}} & (5)\end{matrix}$

Therefore, in order to obtain a step count or intensity level (e.g. “y”)that corresponds to a particular irradiance level (e.g. “x”), thecontrol unit 28 computes the coefficients according to formulas 2, 3, 4and 5 and subsequently computes the desired value from formula 1 asgiven above.

It should be noted that the linearity of the fit will depend upon thetype and configuration of aperture used, the movement of the steppermotor, and so on. Typically, at lower irradiance values where thesignal-to-noise ratio is lower and movement of the stepper motor is lessaccurate, a large number of points will be interpolated. Coefficientscalculated using the spline functions are used for subsequentdeterminations of the step count required to produce a desired outputirradiance (at the end of the light guide) when the delivery device isin subsequent use.

If the calibration sequence was initiated by the radiometer 38downloading a new “desired” irradiance level, the light delivery device10 now will set the stepper motor step count to the count that, when thesplines are taken into account, will produce the desired irradiancelevel at the output of light guide 26, as will be described in moredetail later.

Following calibration of the light delivery device 10, the data memory50 in the radiometer 38 stores ten data entries against the serialnumber for that light delivery device 10, as illustrated in Table I.Each row constitutes a calibration data record and includes entries forthe date and time the measurement was made, the serial number (S/N) ofthe light delivery device 10, the power in watts (W), as measured by thethermopile 44, and the irradiance in W/cm² (as calculated by theradiometer 38 from the current power measurement and the cross-sectionalarea of the current light-guide). An extra column for input channelnumber is optional and indicates whether the radiometer 38 is being usedwith an external radiometer 38 coupled to its RIC port 84 (channel 1) orthe thermopile 44 (channel 0). The radiometer 38 could, of course, stillstore other readings for the same light delivery device from previouscalibrations, but they would have a different time/date.

The radiometer 38 then can be coupled to one or more other lightdelivery devices, in turn, and the calibration process repeated, thegroup of calibration data records for the other delivery devices beingstored as before, but in conjunction with the different serial numbers.

The calibration data records for all of the light delivery devicesstored by the radiometer 38 are accessible to an external computer viathe second RS-232 port 34′ using suitable command software or via it owndisplay 82. Thus, at suitable intervals, for example daily or weekly,the radiometer 38 may download the data to the external computer 86 forstatistical analysis, quality control purposes, archiving, and so on.The data records can be displayed using the same graphical userinterface.

In a production environment, where several light delivery devices havebeen calibrated as described above, the radiometer 38 also can be usedto set several light delivery devices to the same predeterminedirradiance setting. Preferably, whenever a delivery device is being setto a new irradiance level, it will automatically perform the calibrationprocess, so its light guide will already be attached to the radiometer38. Thus, having been calibrated, the first delivery device is adjustedmanually, i.e., using the user interface pushbuttons, so as to set theirradiance measured by the radiometer 38 to a desired (optimum)irradiance for a particular process.

Once the radiometer 38 reads this optimum or “desired” irradiance value,the user presses and holds the STORE button on the radiometer 38 for 5seconds to store the “desired” irradiance setting of the first lightdelivery device 10 into the memory 50 of the radiometer 38.

To set the other light delivery devices to the same irradiance setpoint, the radiometer 38 is connected to each of them in turn,specifically by connecting its optical port to their light guides andits data port to their data ports. Even if the other light deliverydevices have been calibrated, as described above, quite recently, thecalibration will be repeated. The user presses the “CAL” button on theradiometer 38 which then downloads the “desired” irradiance to the lightdelivery device control unit 48 via the data ports.

TABLE I Irradiance Input Date and time Serial # Power (W) (mW/cm²)Channel 2004 Jan. 01, 1:00:00 pm 00001 5.0 25000 0 2004 Jan. 01, 1:00:04pm 00001 5.1 25500 0 2004 Jan. 01, 1:00:08 pm 00001 5.2 26000 0 2004Jan. 01, 1:00.12 pm 00001 5.3 26500 0 2004 Jan. 01, 1:00:16 pm 00001 5.427000 0 2004 Jan. 01, 1:00:20 pm 00001 5.5 27500 0 2004 Jan. 01, 1:00.24pm 00001 5.6 28000 0 2004 Jan. 01, 1:00;28 pm 00001 5.7 28500 0 2004Jan. 01, 1:00:32 pm 00001 5.8 29000 0 2004 Jan. 01, 1:00:36 pm 00001 5.929500 0 2004 Jan. 01, 1:00:40 pm 00001 6.0 30000 0 2004 Jan. 01, 1:06:04pm 00002 5.0 25000 0 2004 Jan. 01, 1:06:08 pm 00002 5.1 25500 0 . . . .. . . . . . . . . . .

As discussed, above, this automatically causes the light delivery device10 to perform the calibration sequence described above and only whenthat has been completed will the light delivery device 10 set its outputlevel (step count) to achieve the desired irradiance. This process isrepeated for each light delivery device of the group.

It should be noted that the feedback control loop (22, 64, 66, 28, 20,16) that compensates for variations in the output of lamp 60 as itdegrades will operate in “real time”.

Whenever a new desired irradiance level is being set, the control unit28 will determine the corresponding step count and intensity level whichcorrespond to the desired irradiance at

TABLE II Step Radiometer Light delivery device 1 User presses CAL buttonon radiometer 38 which initiates communications with light deliverydevice via RS-232 wire or IrDA wireless port 2 Light delivery device 10sends a “ready” command as communications with radiometer 38 have nowbeen opened. 3 Radiometer 38 sends a command for light delivery device10 unit serial number. 4 Light delivery device 10 sends the unit serialnumber to radiometer 38. 5 Radiometer 38 sends a “SET” command to lightdelivery device 10 to select the first one of the predetermined apertureopenings. 6 Light delivery device 10 sends a command to radiometer 38requesting light guide diameter. 7 Radiometer 38 sends the previouslydetermined diameter of the light guide to light delivery device 10. 8The light delivery device 10 opens the aperture means to the first oneof the predetermined aperture openings. 9 The radiometer 38 measurespower and calculates the irradiance using the light guide area. 10 Thelight delivery device 10 sends a request to the radiometer 38 for theirradiance value. 11 The radiometer 38 sends the irradiance value to thelight delivery device 10. 12 The radiometer 38 stores the followingdata: Serial number of current light delivery device 10 Current power inW Current irradiance in W/cm² Current date and time. 13 Repeat steps9-12 for the other 9 predetermined aperture openings. 14 When thedelivery device has completed the last position, it sends a “Done”command to the radiometer 38. 15 Radiometer 38 exits calibrationsequence and returns to normal operation.the output end of the light guide, derived using the splinecoefficients, and then drive the stepper motor to the step count,thereby opening the aperture. The control unit 28 then compares the“desired” digital value S₀′ of the intensity I_(o)′ now being measuredat the photodetector 64 with the “calibrated” digital value, asdetermined using the second spline coefficients. If the “desired”digital value is less, as would be likely if the lamp 60 haddeteriorated since the previous calibration, the control unit 28increases the step count gradually until the “desired” digital intensityvalue is equal to the “calibrated” digital intensity value, therebycompensating for any reduction in the light intensity delivered by thelight source and ensuring that the light leaving the far end of thelight guide 26 has the desired irradiance level.

It will be appreciated that various alternatives and modifications arefeasible without departing from the scope of the present invention.Thus, the light source 12 may comprise known devices such as an arcsource (e.g. mercury, xenon, or mercury/xenon), an incandescent source(e.g. quartz halogen), an “electrode-less” source (e.g. microwavesource), or a solid state light source, e.g. a single light emittingdiode (LED) or a multiple array device.

Generally, the type of light source 12 will be selected according to theapplication. It should be appreciated that a photo-sensitive materialmight require light of having wavelengths and intensity that arecompletely different from those required for performing photo therapy.

In applications where it is not necessary to deliver a focussed orcollimated beam of the light, the fiber optic cable or liquid lightguide can be omitted; for example, where the light source 12 comprises aLED array which illuminates an area.

The detection means 44 could comprise additional optical elements, suchas an integrating cavity and the thermopile 44 shown in FIG. I could bereplaced by some other kind of photodetector, for example a photodiode.Thus, FIG. 4 shows an alternative detection means comprising anintegrating cavity 86, which receives and integrates the light fromlight guide 26 via port 40, and a photodiode 88 for detecting light atan output port 90 of the integrating cavity and supplying thecorresponding electrical signal to A/D converter 46. It should beappreciated that the “desired” irradiance setting could instead beentered into the light delivery device 10 using its own user interfaceand display 32, or, by means of a similar interface displayed on anexternal computer connected to the RS232 data port of the light deliverydevice 10.

It is envisaged that the user interface and the display unit 32 could beadapted to allow the user to initiate the calibration of the lightdelivery device 10.

It will be appreciated that the data could be transferred between theradiometer 38 and the light delivery devices or external computer usingalternatives to the RS232 protocol, such as USB, GPIB, and so on. Itshould be noted, however, that wireless connections, e.g., IrDA, havecertain advantages over data cables because they simplify connection ofthe radiometer 38 to each of several light delivery devices in turn,leading to time savings.

It should also be noted that a variety of aperture configurations andtypes could be used, such as an iris diaphragm, a series of presetapertures or a negative image iris wheel. The preferred type of apertureis a so-called “etched iris wheel”.

The bandpass filter 14 could be any appropriate optical filter and couldbe integrated with other components of the light delivery device 10.

It should also be noted that while ten aperture settings are used forthe calibration process in the above description, any number of aperturesettings may be used. The accuracy of the calibration will, of course,increase with the number of aperture settings used and theirdistribution across the range of operation.

As mentioned above, the light delivery device 10 could be used inrelative mode, i.e., without using the radiometer to associate itsaperture settings with irradiance values using the spline function. Evenso, it would still be possible to use the spline function to calibratethe internal feedback loop that compensates for degradation of the lamp60. In that situation, of course, there would be no series of irradiancemeasurements so the spline would be applied to associate the intensitymeasurements with percentage aperture openings or directly with theaperture step counts.

The invention is not limited to the above-described system and method,or indeed to systems and methods for applying light to photosensitivematerials to initiate curing, drying, hardening or other photosensitivereaction, but comprehends systems and methods for use in otherapplications, for example general illumination, machine vision,photobiology, photodynamic therapy/phototherapy, microscopy, and generalmedical applications, including diagnostic imaging.

Although various preferred embodiments of the present invention havebeen described in detail, it will be appreciated by those skilled in theart that variations may be made without departing from the spirit of theinvention or the scope of the appended claims.

1. A method of setting an output level of a light delivery device (10)that comprises light-emitting means (12), light output means (24; 24,26) for delivering emitted light to a site to be irradiated, intensitycontrol means (16) for adjusting at least the intensity of the deliveredlight, and a memory unit (30) for storing data including parametersindicative of intensity/power level, the light output means (24;24,26)being temporarily connected to a separate radiometer (38) having meansfor detecting power levels of the delivered light, the light deliverydevice (10) and the radiometer (38) having respective control means(28,48) and data communications means (34,36,54,56) for communicatingdata therebetween, the method comprising a calibration sequencecomprising the steps of: (i) with the light output means (24;24,26)coupled to the radiometer (38), establishing data communications betweenthe control means (48) of the radiometer (38) and the control means (28)of the light delivery device (10); at the light delivery device (10):(ii) adjusting the intensity control means (16) successively to each ofa series of predetermined intensity levels; at the radiometer (38):(iii) measuring a series of actual output irradiance levels delivered bythe light output means (24;24,26), each for a respective one of saidpredetermined intensity levels; (iv) transmitting the actual outputirradiance levels to the light delivery device (10); at the lightdelivery device (10): (v) associating each of the actual outputirradiance level measurements with the corresponding intensity levelparameters in said memory unit.
 2. A method according to claim 1,wherein the step of adjusting the intensity control means (16)successively to each of a series of predetermined intensity levelscomprises setting a variable aperture unit (18) of the intensity controlmeans (16) to each of a series of different aperture openings.
 3. Amethod according to claim 1, further comprising the step of; (vi)applying a best fit algorithm to the actual irradiance levelmeasurements and corresponding predetermined intensity level parametersand using the best fit parameters to select subsequent desired outputirradiance levels.
 4. A method according to claim 1, wherein, in asubsequent step of setting the light delivery device (10) to deliver adesired output irradiance level, the intensity level of light downstreamof the output of the intensity control means (16) is measured, comparedwith a reference, and the intensity control means (16) adjusted tocorrect for any differences between the measured intensity level and thereference.
 5. A method according to claim 3, further comprising thesteps of; obtaining, for each of said series of predetermined intensitylevel parameters, a corresponding series of measurements of intensitylevel of light downstream of the output of the intensity control means(16), applying a best fit algorithm to the actual irradiance levelmeasurements and corresponding parameters; applying a best fit algorithmto the actual intensity level measurements and said actual irradiancelevel measurements; in a subsequent intensity level setting step,setting the intensity level to the desired setting, measuring the saidactual intensity level again, comparing the measured-again intensitylevel with the intensity level for that desired irradiance levelaccording to the best fit algorithm, and adjusting the intensity controlmeans (18) to correct for any differences.
 6. A method according toclaim 1, wherein, when establishing communications, the radiometer (38)acquires from the light delivery device (10) a unique identifier, suchas its serial number, and stores the irradiance measurements inassociation with said unique identifier in a memory unit (50).
 7. Amethod according to claim 6, wherein each of the irradiance measurementsis stored in association with temporal information identifying when suchmeasurement was made.
 8. A method according to claim 1, the light outputmeans comprising a light guide (26) coupled to an optical output port(24) of the light delivery device (10), the method further comprisingthe step of determining the diameter of the light guide (26) and usingthe measured power and the effective cross-sectional area, derived fromthe diameter, to compute the irradiance of the delivered light.
 9. Amethod according to claim 7, wherein the computation of the irradianceis performed at the radiometer (38).
 10. A method according to claim 8,wherein the radiometer (38) stores effective diameters of a plurality ofdifferent types of light delivery means, the light delivery means of aparticular type having the same effective cross-sectional area, andbeing associated with an indicator unique to that type, and the step ofdetermining the effective cross-sectional area includes the steps ofdetecting a said unique indicator of said light delivery means connectedto the optical input port, using the detected indicator to retrieve theeffective diameter for that light delivery means from storage andcalculating the cross-sectional area from that effective diameter.
 11. Amethod according to claim 10, wherein the unique indicator is colour ofa colour-coded adapter (42) specific to the type of light delivery means(26) and the step of detecting said unique indicator includes the stepof determining the colour of the colour-coded adapter (40) connectingthe light delivery means (26) to the optical input port (40).
 12. Amethod according to claim 1, further comprising the step of repeatingthe calibration sequence for each of a plurality of other similar lightdelivery devices (10) and setting the plurality of other similar lightdelivery devices to the same output level by coupling the radiometer(38) to each of the light delivery devices (10) in turn, outputting fromthe radiometer (38) to the control means (28) of the light deliverydevice (10) a desired irradiance value previously stored in theradiometer (38); and storing the light irradiance value in the memory(30) of the light delivery device (10), each light delivery device (10)using the stored irradiance value for subsequent operation.
 13. A methodaccording to claim 12, wherein the desired irradiance is obtained by theprior step of measuring an actual irradiance level outputted by one ofthe light delivery devices, or a similar light delivery device, manuallyadjusting the light delivery device until the actual irradiance level isacceptable, and storing the accepted irradiance level as said desiredirradiance level for supplying to the other light delivery devices. 14.A method according to claim 1, wherein the data communications link isestablished by way of wireless input/output ports of the light deliverydevice (10) and radiometer (38), respectively.
 15. A method of settingrespective output light irradiance levels of a plurality of lightdelivery devices to the same irradiance level using the same radiometer,each light delivery device comprising light-emitting means, output meansfor supplying the emitted light to a site to be irradiated, intensitycontrol means (16) for adjusting at least the intensity of the deliveredlight, a memory unit for storing parameters indicative of intensitylevels and control means for controlling the intensity control means,the radiometer having data storage means for storing data includinglight irradiance values, the radiometer and light delivery deviceshaving data communications means for communicating data therebetween,the method comprising the steps of: (i) manually adjusting a first lightdelivery device to deliver a desired irradiance level at its outputmeans; (ii) temporarily coupling the radiometer to the output means ofthe first light delivery device and measuring said desired irradiancelevel; (iii) storing said desired irradiance level in the memory of theradiometer; (iv) temporarily coupling the radiometer to the output meansof at least a second such light delivery device, and transmitting saiddesired irradiance level to said second delivery device via said datacommunications means; and (v) storing the light irradiance value in thememory of the second light delivery device for future use in normaloperation.
 16. A method according to claim 14, further comprising theprior step of calibrating each of the light delivery devices with theradiometer (38) so that irradiance levels correspond to aperturesettings.
 17. A method according to claim 15, wherein the datacommunications link is established by way of wireless input/output portsof each light delivery device and the radiometer (38), respectively. 18.A method of setting respective output light irradiance levels of aplurality of light delivery devices (10) to the same irradiance levelusing the same radiometer (38), each light delivery device (10)comprising light-emitting means (12), output means (24; 24, 26) forsupplying the emitted light to a site to be irradiated, intensitycontrol means (16) for adjusting the irradiance of the delivered light,a memory unit for storing irradiance levels, and control means (28) forcontrolling the intensity control means (18), the radiometer (38) havingdata storage means (50) for storing data including light irradiancevalues, the method comprising the steps of: temporarily coupling theradiometer (38) to the output means of each light delivery device inturn, and outputting to each said light delivery device a desiredirradiance level previously stored in the memory of the radiometer (38);and storing the light irradiance value in the memory unit of each saidlight delivery device (30) for future use in normal operation.
 19. Amethod according to claim 18, wherein the radiometer is coupled to thelight delivery device by means of a wireless data communications link.20. A radiometer (38) for use in setting output light delivered by atleast one light delivery device (10) to a desired light irradiancelevel, said at least one light delivery device comprising light emittingmeans (12), light output means (24; 24, 26) for supplying the emittedlight to a site to be irradiated, intensity control means (16) foradjusting the irradiance of the delivered light, a memory unit forstoring irradiance levels, and data communications means (28, 34, 36),the radiometer (38) comprising: means for measuring an irradiance levelof light delivered by said light output means of said light deliverydevice; data communications means (48, 54, 56) complementary to the datacommunications means (28, 34, 36) of the light delivery device, andcontrol means (48) for establishing data communications with a lightdelivery device (10) coupled thereto and for outputting to said lightdelivery device (10) said desired light irradiance value from saidmemory via the data communications means.
 21. A radiometer according toclaim 20, further comprising storage means (50) for storing a pluralityof said desired irradiance values in association with a uniqueidentifier, for example serial number, of a said light delivery device(10), and wherein the control means is operable to obtain said uniqueidentifier from said light delivery device via said data communicationslink.
 22. A radiometer according to claim 20, further comprising datacommunication means for communicating stored data to an externalcomputer.
 23. A radiometer according to claim 20, wherein the datacommunications means is wireless.
 24. A radiometer according to claim20, further comprising means for detecting an identifier of a lightoutput means connected thereto, said identifier indicating that thelight output means has a particular diameter, the control means beingoperable to use the identifier to determine the cross-sectional area anduse the cross-sectional area and measured power to compute theirradiance of the delivered light.
 25. A radiometer according to claim24, wherein the identifier is the colour of a colour-coded adapter forconnecting the light output means to the radiometer, and the detectingmeans is configured to detect the colour of the adapter and supplycolour coordinates to the control unit, the memory unit storing coloursand corresponding diameters or areas of the light output means.
 26. Aradiometer according to claim 25, wherein the detecting means comprisesa colorimeter.
 27. A light delivery device comprising light-emittingmeans, light output means for delivering the emitted light to a site tobe irradiated, intensity control means (16) for adjusting irradiance ofdelivered light; and control means for controlling the intensity controlmeans and for communicating with an external radiometer, the controlmeans being operable to adjust the intensity, successively, to aplurality of intensity levels and, for each intensity level, communicatewith the radiometer to obtain from the radiometer a corresponding seriesof actual irradiance levels measured by the radiometer and store eachirradiance value in a memory unit in association with the correspondingintensity level.
 28. A light delivery device according to claim 27,wherein the intensity control means (16) comprises a variable apertureunit (18) for selecting each of a series of different aperture openingsto set the intensity level, the stored parameters then comprisingaperture settings.
 29. A light delivery device according to claim 28,wherein the control means is operable to apply a best fit algorithm tothe actual irradiance level measurements and corresponding aperturesettings and use the best fit aperture settings to select subsequentdesired output irradiance levels.
 30. A light delivery device accordingto claim 28, further comprising means for measuring the intensity levelof light downstream of the output of the intensity control means (16),the control means being operable to associate a series of intensitymeasurements with said series of irradiance measurements and, whensubsequently setting the intensity of light outputted by the lightdelivery device (10) to deliver a desired output irradiance level, setthe intensity to an initial setting corresponding to the desiredirradiance level, measure the actual intensity level and compare suchactual intensity level with the associated intensity level and adjustthe intensity control means (16) to correct for any differences betweenthe measured actual intensity level and the associated intensity level.31. A light delivery device according to claim 30, further comprisingmeans for measuring the intensity level of light downstream of theoutput of the intensity control means (16), the control means beingoperable to associate a series of intensity measurements with saidseries of irradiance measurements and perform a best fit algorithm toassociate intensity measurements with irradiance measurements and, whensubsequently setting the intensity control means of the light deliverydevice (10) to deliver a desired output irradiance level, set theintensity to an initial setting corresponding to the desired irradiancelevel, measure the actual intensity level and compare such actualintensity level with the associated intensity level and adjust theintensity control means (16) to correct for any differences between themeasured actual intensity level and the associated intensity level. 32.A light delivery device according to claim 28, wherein the variableaperture means (18) is adjustable between a completely closed conditionand a variety of open areas, the control means (28) being operable toswitch the variable aperture means (18) from a closed state to aselected one of the open sizes, and back to the closed state todetermine exposure period.
 33. A light delivery device according toclaim 28, wherein the control means compensates for aperture opening andclosing delays when determining exposure times.
 34. A light deliverydevice comprising light-emitting means (12), light output means (24; 24,26) for delivering the emitted light to a site to be irradiated,intensity control means (16) for adjusting irradiance of deliveredlight, detection means for detecting intensity of light downstream ofthe output of the intensity control means and control means (28) forcontrolling the intensity control means (18), wherein the control means(28) is operable to: monitor the detection means and determine, for eachof series of predetermined intensity level settings, a correspondingseries of measurements of intensity level of light downstream of theoutput of the intensity control means (16), apply a best fit algorithmto the actual intensity level measurements and said intensity levelsettings; and in a subsequent intensity level setting step, adjust theintensity level to the desired setting, measure the said intensity levelagain, compare the measured-again intensity level with the intensitylevel for that intensity level setting according to the best fitalgorithm, and adjust the intensity control means (16) to correct forany differences.